Ab initiocalculation ofH+He+charge-transfer cross sections for plasma physics

Abstract

The charge-transfer in low-energy ($0.25$ to $150$ eV/amu) $\mathrm{H}(\mathit{nl})+{\mathrm{He}}^{+}(1s)$ collisions is investigated using a quasimolecular approach for the $n=2,3$ as well as the first two $n=4$ singlet states. The diabatic potential energy curves of the HeH${}^{+}$ molecular ion are obtained from the adiabatic potential energy curves and the nonadiabatic radial coupling matrix elements using a two-by-two diabatization method, and a time-dependent wave-packet approach is used to calculate the state-to-state cross sections. We find a strong dependence of the charge-transfer cross section on the principal and orbital quantum numbers $n$ and $l$ of the initial or final state. We estimate the effect of the nonadiabatic rotational couplings, which is found to be important even at energies below $1$ eV/amu. However, the effect is small on the total cross sections at energies below $10$ eV/amu. We observe that to calculate charge-transfer cross sections in an $n$ manifold, it is only necessary to include states with ${n}^{\ensuremath{'}}\ensuremath{\leqslant}n$, and we discuss the limitations of our approach as the number of states increases.